Apparatus for the integrated welding and heat treating of hardenable parts



April 14, 1970 P. M. SAMPATACOS HARDENABLE PARTS 2 Sheets-Sheet 1 Original F'iled Sept. 1.9, 1966 APPARATUS FOR THE INT-EGRA'ED WELDING AND BEAT TREATING OF 2 SheetsShee': 2

HARDENABLE PARTS Original Filed Sept. 1.9, 1966 ATTORNEY Unted States Patent U.S. Cl. 2664 4 Claims ABSTRACT OF THE DISCLOSURE Apparatus is disclosed for welding and for heat treating hardenable metal workpieces which are at least partally annular or ring-like in configuration, such as hearing rings. In a preferred form the apparatus is formed of a cylindrical mandrel, a concentric annular sleeve disposed ahout the mandrel to define an annular working charnher having a workpiece inlet end and a workpiece outlet end, and a quenching chamher extending downwardly from the werking chamher a barometric height into a sump containing a quenching liquid. Suitahle means for heating and/or welding the workpieces and for evacuating the working and quenching chamhers are provided.

This is a division of S.N. 580,284 filed Sept. 19, 1966. My invention relates generally to welding and heat treating hardenable material and more particularly to a method and apparatus to concurrently effect a welded joint hetween two ferrous alloy memhers and heat treat the entire structure. My invention is especially suitahle for, hut not limited to, the manufacture of hearing ringsor races.

For some time, the economic advantages of the following general method of hearing manufacture has been recognized. This method comprises forming strip or har stock to approximately the desired final cross sectional shape of a hearing race (such formng including rolling, drawng or other means suitable to form a raceway or the like in the strip), cutting the formed strip to a suitable length, hending the cut strip to circular or semicircular configuration and weldng abutting ends to complete the hearing race. This method virtually eliminates the generation of scrap and many of the grinding and machining operations associated with conventional hearing race manufacturing techniques. The aforementioned method while known for some time as exemplified by the expired patent to Hess 1,967821, has not yet found commercial acceptance. The reluctance on the part of the purchaser and manufacturer is due mainly to fear of premature hearing ring -failure at the welded joint. The fear is based on the fact that the hearing sections to he joined (as Well as sections of other welded articles) are usually heated only in the vicinity of the weld so that the metal, as for example steel hearing alloy, adjacent the weld selectively undergoes phase transformation and volume change resulting in residua] stresses and an undesirahle grain structure and microstructure. Even when heat has been more uniformly applied hy prior art techniques the undesirahle residual stresses in ferrous hearing alloys have not been completely eliminated. While these latent defects in the structure adjacent the weld can be corrected to some extent by additional working of the part, experience has shown the discriminating purchaser that the weakness of the hearing still lies in the weld area and that this weakness is most easily circumvented hy purchasing hearings made hy older and more costly techniques. The older techniques generally 3,56251 Patented Apr. 14, 1970 comprise a numher of forming and grinding operations with the metal in a relatively soft condition followed hy separate heat treating steps te harden the steel. In addition to these older techniques heing more costly due to material scrappage and high fabrication time, additional time and oost are involved in a hardening heat treatment of the part at the point of almost complete manufacture.

It is an object of my invention to provide a method of concurrently welding and heat treating hardenable ferrous metal alloys whereby there are no localized phase transformations and volume changes therehy significantly improving the strength and quality of the weld and of the entire structure.

It is another object of my invention to provide a process and apparatus which, in a preferred emhodiment, are especially suitable for making hearing races, which bearing races are made with a welded joint and concurrently heat treated therehy eliminating many time consuming and costly steps from other conventional manufacturing methods. In addition, a hearing made hy my invention virtually eliminates the formation of scrap While the end product consistently demonstrates greater endurance and capacity than rings from conventional rnanufacturin g techniques.

A more specific object of my invention in terms of a preferred embodiment is to provide a method and apparatus for welding steel hearing races in which the steel is welded in the austenitic condition and is thereafter quenched to a predetermined condition of hardness and microstructure therehy integrating the welding and heat treatment of the steel into a simpler and cheaper operation.

Other ohjects and advantages of my invention will hereinafter -become more fully apparent from the following description of the annexed drawings which illusstrate oreferred embodiments and wherein:

FIGURE 1 is a time-temperature curve illustrating the steps of my process. Included as a part of this figure is a tirne-temperature-transformation curve for SAE 52100 steel, a commonly used hearing steel, showing the time-temperature phase transformation relationship which a steel part undergoes after welding when processed in accordance with my invention;

FIGURE 2 is a schematic view partly in section and partly broken away, of apparatus in accordance with my invention capable of carrying out my welding-heat treatment process;

FIGURE 3 is a sectional view of a portion of the apparatus shown in FIGURE 2 as viewed along line 33 of F IGURE 2; and

FIGURE 4 is also a sectional view of a difierent portion of the apparatus of FIGURE 2 as viewed along line 44.

Referring to the time-temperature curve of FIGURE 1, I will now explain the steps of my invention relative to the welding and heat treating of a steel hearing race partially manufactured hy the old known technique of forming a hearing race from strip stock which is bent to circular or semicircular form and in which the ends are to be butt welded.

My invention is primarly directed toward the steps of welding and heat treating the hearing rings thus formed. I preferahly use two semicircular hearing halves which require two weids at diametrically opposite jonts. In order to circumvent the undesirahle localized phase transformations and volume changes I heat the hearing halves above their austenitic transformation temperature (Ae in FIGURE 1), the temperature for a given steel a=hove which the alloy completely transforms to austenite. This temperature varies depending on the type of steel heing used. As part of FIGURE 1, I have shown in isothermal transformation curve for SAE 52100 steel which is a typical hearing steel. This is an electric furnace steel and its ladle chemical composition limits are commonly specified to he, by weight: 0.95 to 1.0% carbon, 0.25 to 0.45% manganese, up to 0.024% phosphorus, up to 0.025 sulfur, 0.20 to 0.35% silicon, 1.30 te 1.60% chromium, and the halance suhstantially all iron. However, nickel is sometimes incorporated up to about 0.20 to 0.25% hy Weight. The upper critical limit (A2 for this alloy is approximately 1550 F. In accordance with my process the hearing ring halves are heated ahove the upper critical temperature for a suflicient time to completely austenitize the steel throughout the parts. Here again, the time to austenitize the part will depend on the type of steel with the exact time necessary for a given steel heing easily determinable trom standard charts. Once the parts have been austenitized, the ahutting ends are welded while the halves are mantained austenitic. In order to prevent oxidation of the halves while heing welded, they are preferably placed in a vacuum environment and the weld is accomplished hy directing an electron heam at the junctures of the abutting edges. Electron heam welding is descrihed in the patent issued to Steigerwald, U.S. 2,987,610. This type of welding is preferred in my process because beams of electrons can be focused on a very small area at the joint and the technique is very etlicient. In welding with electron beams I preferably used a pulsed application of the heam to reduce locally excessive temperatures and vapor formation during welding thereby eliminating weld deficiencies. The halves are mantained austenitic during welding within a vacuum environment. Thus, no part of the workpiece, except for the solidifying metal, undergoes phase transformation until after the weld has been completed. The assemhly may then be quenched and hardened without further heating. In the emhodiment of my invention which is now heing clescrihed the welded race is quenched in a nonoxidizing environment, such as for example a bath of a molten salt, a suitable oil, liquid lead, or other suitable liquid metal, from above the upper critical limit to a predetermined temperature to obtain a desired condition of hardness. The race may then be additionally cooled prior to heing exposed to an oxidizing atmosphere. The quenching may he followed hy tempering as necessary or desired.

The specfic preferred treatment to which hearing races are suhjected is as shown in FIGURE 1. After welding the race is martempered, that is, it is liquid quenched to approximately 500 F. in about eight seconds and maintained there for approximately one minute hefore heing exposed to an oxidizing atmosphere. This rate of cooling is sufficient to completely miss the nose of the TTT diagram and avoid the undesirable phase transformation of austenite to ferrite and cementite. As stated, the quench bath is mantained at about 500 F. slightly ahove the M (martensite start limit) temperature. The race is suhsequently cooled in air or a controlled atmosphere to approximately room temperature over a period of about one hour during which time the austenite transforms into martensite, a microstructure having a high hardened characteristic. After the race has been transformed to this grain structure, the race is tempered to the desired combination of toughness and hardness hy elevating its temperature to just below the M line for a time and then cooling. The above-descrihed hardening of the steel is known as -martempering. Of course, other heat treat cycles could he suitably used in accordance with my invention suhsequent to the welding step. In each case the temperature of the quench bath and/or the rate of cooling for a specific heat treatment and a specific ferrous alloy may he obtained trom sotherrnal transformation data of the type depicted in FIGURE 1 for SAE 52100 steel. This information is availahle in various texthooks, journals, and handhooks and is readily interpreted by competent metallurgists. An advantage of my method is that there is no localzed phase transformation or V01- ume change in the welded part (other than the solidification of the molten alloy at the weld) and the completely austenitic material may -he converted immedately to a desired microstructure and grain size without further heating.

In FIGURES 2, 3 and 4 I have shown an apparatus 12 which is suitable for use in a preferred emhodiment of my welding-heat treatment process; the joining of preformed semicircular hearing race memhers. As best seen in FIGURE 2, a suitable cylindrical ceramic or high temperature metal mandrel 14 is provided such that pairs of semicircular hearing race memhers may be snugly positioned around it in ahutting relationship and moved along its surface trom left to right. Over most of its length the mandrel 14 is sealed Within a housing 22 so that the environment within the enclosed space may he controlled in a predetermined manner. Within the housing 22 is a circular ceramic or refractory alloy sleeve 18 which is concentrically disposed about the mandrel 14 in spaced relationship thereto. The porosity of the mandrel 14 and sleeve 18 may, if desired, he controlled to permit injection of argon, nitrogen, helium or other suitable inert gas into the space about the rings 20. The respective dimensions of the mandrel 14 and the sleeve 18 are such that the semicircular ring members 20 may he moved along the mandrel 14 while clearing the inner cylindrical surface of the sleeve hy only a few thousandths of an inch. Sealing means can he provided at each end of the housing 22 so that a vacuum may he mantained within the apparatus 12 while the semicircular ring memhers 20 are continuously introduced thereto and withdrawn therefrom. At the left end of the apparatus as shown in FIGURE 2, which is the point at which the ring memhers are introduced, the housing 22 is closed by a gate 24 which includes a flexihle annular seal 26. The flexihle seal 26 hears against the steel ring memhers which are being moved along the mandrel 14. At the right end of the housing 22 a seal is mantained by a barometric height of liquid 66 which will he discussed in more complete detail below.

As shown in FIGURE 2 the mandrel 14 is suitably mounted at the left end on a stationary support 16. Viewing from the left end to the right end of the apparatus 12 it is ohserved that the continuity of the sleeve 18 is interrupted hy a plurality of annular stations or chamhers 28, 32, 35, 44 and 50 within the housing 22. These chamhers 28, 32, 35, 44 and 50 are interconnected because of the clearance hetween the semicircular rings 20 and the sleeve 18 and they are used in comhination with heating and pump means to provide a suitable environment for carrying out the process of my invention. The first annular chamher 28 is evacuated hy a mechanical pump 30 as shown, or hy other suitable means such as a multistage steam ejector. The second chamher 32 is also evacuated hy a mechanical pump 34. In normal operation it is preferred that the absolute pressure in the first chamher 28 he below about 500 microns of mercury and the absolute pressure in the second chamher 32 about microns of mercury. A third chamher 35 is evacuated hy a dilusion pump 36 to an absolute pressure of about 1 micron. Chamher 35 houses a pair of electron heam heaters 38 each of which comprises a thermionic emitting heated filament or coil 40 and an electron heam control shield 42. Filament 40 is maintained at a high negative potential and the shield 42 is mantained at an intermediate potential to permit control of the shape of the electron beam. The electron heam is thus accelerated to the rings 20, which are at ground or zero potential, bomharding and thus heating them.

Next is chamher 44 which houses a pair of diametrically opposed electron heam welders 48 and is evacuated by a diifusion pump 46. The operative pressure in chamher 44 suitably is below 1 millimeter of mercury and preferably is below about 0.5 micron. A second pair of electron heam heaters 54 are disposed in chamher 50 which is evacuated hy a diffuson pump 52. Although it is not specifically shown in FIGURE 2, it is to be understood that diflusion pumps are typcally hacked up by a mechanical pump. The chamher 56 at the end of the ceramic mandrel 14 and sleeve 18 is evacuated by a mechanical pump 58 and contains a plunger 60 driven hy a pneumatic or hydraulic motor 62. The lower end of chamher 56 is disposed in a sump 64. The sump and lower portion of chamher 56 are filled with a quenching liquid 66. Since the chamher 56 is at a low absolute pressure, well helow one millimeter of mercury, and the sump 64 is exposed to the atmosphere, the quenching liquid rises to approximately a harometric height H in the lower end of chamher 56. A suitahle conveyor 68 runs through the quenching liquid to remove the races from it to the atmosphere.

Referring now to the left-hand end of the figure, its mode of operation in practicing a preferred emhodiment of my weldingheat treat process will be explained. A pair of semicircular hearing rngs 70 and 72 are shown. These hearing rings which have already been formed to the desired cross sectional shape and size are fed onto the central mandrel 14 at the left-hand end hy a suitahle feed mechanism (not shown). It is to he understood that the offset relationship of the hearing halves 70 and 72 is for the purposes of illustration only and that in actual practice, these hearing halves would he aligned with their ahutting edges lying in a plane of the drawngs at least hy the time they reach the welding guns 48. The pumps 30, 34, 36, 46, 48, 52, and 58 evacuate the entire housng to a low absolute pressure. Because there is only a few thousandths of an inch clearance between the hearing parts 20 and the annular space defined between mandrel 14 and the sleeve 18, the pumps are able to maintain ths vacuum even though some leakage occurs between the races and the mandrel and outer sleeve. The vacuum in the apparatus draws the parts inwardly toward the right. If desired, a suitahle guide 74 (as shown in FIGURE 3) to assure alignment of the hearing halves and a suitable feed rate mechanism 76 (shown in FIGURE 4) may he included to regulate the feed rate of the races. As shown in the drawings, the entire space between the mandrel 14 and sleeve 18 is filled with pairs of hearing halves 20 in end to end ahutting relationship. The hearing halves are fed to the right along the mandrel in a vacuum environment. At chamher 35, the races are heated by electrons emitted from coil 40 of the heater 38 and directed toward the hearing halves hy the shield 42. The energy level of the electron beam heater and the fed rate are adjusted so that the steel race parts are completely austenitized by the time they reach the next station or chamher 44 containing the electron beam welder 48. In the chamher 44 the semicircular austenitized steel hearing halves have the ahutting edges welded together as they pass together under the beam. Commercially availahle welders provide for focusing and aiming of the beam at the exact juncture of the ahutting edges. As previously stated, the electron beam is preferably applied in a pulsed manner so that the parts are not heated excessively and so that the vapors formed hy the welding are allowed to escape during the nonapplication periods. The period of pulsing is roughly one to ten, that is, one time period of application for every nine time periods of nonapplication. Of course, this is an approximate figure and the exact pulsing mode may vary from 5% on, 95% ofi to 95% on, 5% ol depending on the desired welding conditions, and the material heing welded, the geometry of the part heing welded and the feed rate of the parts past the welding gun. After having heen welded, the 52100 steel hearing parts are maintained austenitic by the second electron beam heater 54 in chamher 50 and in a vacuum environment. Shortly thereafter and while still austenitic, the parts reach the end of the mandrel. Because of the continuous weld a completed race 78 must he separated from the adjacent one as it comes o the end of the mandrel. This is easily acc0mplished hy a timed actuation of the motor 62 to move plunger 60 to break away each hearing ring as it comes off the end of the line. Note also that the chamher 56 is at vacuum so that the parts have been in a nonoxidizing environment up to this point. As the plunger knocks the end hearing ring 78 ot, it alls into the quenching liquid 66. The quenching liquid is selected for a desired quenching temperature and cooling rate for the part which in turn are determined hy the desired microstructure and condition of hardness. Other criteria for the selection of the quench are compatibility for material heing quenched, vapor pressure characteristics and specific gravity. The vapor pressure affects the vacuum level and specific gravity affects height H of the harometric leg. After the welded part 78 falls into the quenching hath 66, it is pcked up hy the conveyor 68 and hrought out into the atmosphere for a suhsequent air cooling. The parts may then he taken off the helt and tempered, if desired.

Of course, one skilled in the art would recognize that ferrous alloys other than SAE 52100 steel may advantageously be welded and heat treated in accordance with my process. Any ferrous-hased composition as for example steel, including stainless steels, or cast iron which may be austenitized hy heating and suhsequently hardened hy quenching or other means of rapid cooling, may he so treated. Also in some cases it may not be required that the steel he through hardened. It may he preferred to anneal the steel rather than fully harden it. In this event the temperature of the quench hath could suitahly be kept ahove the transformation temperature for the complete anneal of the parent metal and weld metal. After removal from the quench hath, the workpieces are sl0w cooled at a rate to ohtain a full anneal.

Within the scope of my invention any welding means wherehy two ferrous alloy memhers are first heated into the austenite region and then further heated up to the molten state at the surfaces to he joined, with or without the addition of filler metal, could he used in accordance with my invention. Thus, the energy for meltng ferrous alloys can be provided hy such well known processes as metallic arc welding, carbon arc welding, atomc hydrogen welding, an acetylene gas flame, oxy-acetylene flame, oxy-hydrogen and the like, as well as electron beam weld- 1ng.

It is also to he understood that the welding and heat treating environment can he other than a vacuum. Where oxidation is a problem a protective inert atmosphere of helium or argon may be provided. In other cases the process may he conducted rapidly under atmospheric conditions.

Therefore, while my invention has been descrihed in terms of a preferred emhodiment, the scope thereof is to he limited only hy the following claims.

I claim:

1. Welding-heat treating apparatus for joining hardenahle metallic members comprising, in comhination, an elongated mandrel adapted to carry hardenahle, at least partially annnlar metallic workpieces thereon for welding ahutting surfaces of a said workpiece,

a sleeve disposed about said mandrel enclosing a length wise portion thereof and spaced therefrom to define a werking chamher between said mandrel and said sleeve of cross section just suflicient to provide clearance for the movement of a numher of said workpieces through said work chamher on said mandrel, said working chamher having a workpiece inlet at one end thereof in communicaton with the atmosphere and a workpiece outlet,

welding means communicating with said work chamher,

heating means communcating with said work chamher,

a quenching chamher communcating with said workpiece outlet of said working chamher and extending downwardly therefrom at least a harometric height, means for evacuating atmospheric gases from said working chamher and said quenching chamher,

and a sump containing a quenching liquid, said sump dsposed adjacent the 1ower end of said quenching charnber with the lower end of: said quenching chamber being submerged in said liquid.

2. Welding-heat treating apparatns for joining abutting surfaces of at least partally ring-lke hardenable metallic members comprising, in combination, a cylindrical central mandrel, a concentrc annular sleeve spaced from said mandrel to form an annular chamber, heating means communicating with said annular chamber adjacent one end thereof, weldng means communcating with said annular chamber =between said heating means and the opposite end of sadannular chamber, a second chamber communicating with said opposite end of said annular chamber and extendng therebelow at least a barometrc heght, means to evacuate said chambers, and a sump containing a liquid disposed adjacent the lower end of said second chamber, said lower end being submerged in said liquid.

3. The apparatus of claim 2 wherein said mandrel is provided with axially extending gude means to assure alignment of said hardenable metallic members in said annular chamber.

4. The apparatus of claim 2 wherein feed rate controling means is provided to control the rate of movement of said hardenable metallic members through said annular chamber along said mandrel.

References Cited UNITED STATES PATENTS J. SPENCER OVERHOLSER, Primary Examiner R. S. ANNEAR, Assstant Examner U.S. C1. X.R. 

